MOF-derived Co3O4 thin film decorated BiVO4 for enhancement of photoelectrochemical water splitting

Bismuth vanadate (BiVO4) with narrow bandgap was considered as one of the most desirable matrices for photoanode in photoelectrochemical (PEC) water splitting system. However, the poor charge separation in BiVO4 causes the practical PEC efficiency significantly lower than the theoretical value. Herein, we demonstrated an effective strategy for growing positively charged Co-MOF (ZIF-67) onto the surface of BiVO4 photoelectrode via the electrostatic attraction with negatively charged BiVO4. Then the Co-MOF-BiVO4 photoelectrodes were annealed and a uniform Co3O4 thin film was formed on the BiVO4 photoelectrode. Compared with the bare BiVO4 photoanode, the best photocurrent density of Co3O4/BiVO4 photoanode reached up to 2.35 mA/cm2 (1.23 V vs RHE), with an incident photon to current conversion efficiency (IPCE) of 26% (360 nm). The PEC hydrogen production of Co3O4/BiVO4 was 0.61 mmol/cm2 in 5 h (100 mW/cm2, 1.23 V vs RHE), which was almost 3.2 times higher than that of bare BiVO4. The significant enhancement of PEC performance over Co3O4/BiVO4 photoanodes could be attributed to the unique structure characteristics of the in-situ MOF-derived Co3O4 thin film, with extend surface area and increased number of active sites.